U.S. patent number 7,009,922 [Application Number 10/105,946] was granted by the patent office on 2006-03-07 for cross-talk removal apparatus and data reproduction apparatus.
This patent grant is currently assigned to Pioneer Corporation. Invention is credited to Hiroki Kuribayashi, Shogo Miyanabe.
United States Patent |
7,009,922 |
Miyanabe , et al. |
March 7, 2006 |
Cross-talk removal apparatus and data reproduction apparatus
Abstract
In a cross-talk canceller (CTC) that removes the cross-talk from
the adjacent tracks that is contained in the reproduction signal
from the main track, a sample-value series S1' for the reproduction
signal from the adjacent track is input to a correlation-detection
unit to find its correlation with the signal pattern of the signal
output from the CTC that is detected by a pattern-detection unit,
and then it passes through one of the correction-coefficient units
that is connected by the switch and then integrated by the
integrator, and the tap coefficient used by the variable filter of
the CTC is obtained to a narrow control frequency zone.
Inventors: |
Miyanabe; Shogo (Tsurugashima,
JP), Kuribayashi; Hiroki (Tsurugashima,
JP) |
Assignee: |
Pioneer Corporation (Tokyo-To,
JP)
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Family
ID: |
18979775 |
Appl.
No.: |
10/105,946 |
Filed: |
March 26, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20020159313 A1 |
Oct 31, 2002 |
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Foreign Application Priority Data
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Apr 27, 2001 [JP] |
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P2001-131620 |
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Current U.S.
Class: |
369/47.17;
369/53.33; G9B/20.01 |
Current CPC
Class: |
G11B
20/10009 (20130101) |
Current International
Class: |
G11B
20/24 (20060101) |
Field of
Search: |
;369/47.17,53.33 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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5166914 |
November 1992 |
Shimada et al. |
5835467 |
November 1998 |
Tomita et al. |
6687204 |
February 2004 |
Miyanabe et al. |
|
Primary Examiner: Hudspeth; David
Assistant Examiner: Giesy; Adam R.
Attorney, Agent or Firm: Drinker Biddle & Reath LLP
Claims
What is claimed is:
1. A cross-talk removal apparatus that removes cross-talk from one
or the other or both adjacent tracks, which is contained in the
reproduction signal from a main track on a data-recording medium
that is to be reproduced, based on the reproduction signal from
said main track and the reproduction signals from said one or the
other or both adjacent tracks and comprising: a cross-talk removal
device of using a variable filter with a controllable coefficient
to extract the cross-talk from the reproduction signal of said one
or the other or both adjacent tracks and removing said cross-talk
from the reproduction signal of said main track; a coefficient
control device of controlling the coefficient of said variable
filter using a changeable control frequency zone; and a control
frequency zone setting device of determining the recording state of
said one or the other or both adjacent tracks and switching said
control frequency zone according to said recording state, wherein
said control frequency zone setting device sets said control
frequency zone to be wide for a specified period of time when the
recording state of said one or the other or both adjacent tracks
changes from an non-recorded state to a recorded state.
2. The cross-talk removal apparatus of claim 1 wherein said
coefficient control device is capable of switching said control
frequency zone between a first control frequency zone and a second
control frequency zone that is wider than said first control
frequency zone, and wherein said control frequency zone setting
device normally sets said first control frequency zone, and sets
said second control frequency zone for a specified period of time
when the recording state of said one or the other or both adjacent
tracks changes from an non-recorded state to a recorded state.
3. The cross-talk removal apparatus of claim 2 wherein said
specified period of time is the time required for said coefficient
to converge when said second control frequency zone has been
set.
4. The cross-talk removal apparatus of claim 1 wherein said control
frequency zone setting device determines the recorded state and
non-recorded state based on the amplitude of the reproduction
signals from said one or the other or both adjacent tracks.
5. The cross-talk removal apparatus of claim 1 wherein said control
frequency zone setting device sets said control frequency zone to
zero when the recording state of said one or the other or both
adjacent tracks changes from a recorded state to a non-recorded
state.
6. A data reproduction apparatus that reproduces recorded data from
a data-recording medium on which tracks are formed and comprising:
a reproduction device of generating a reproduction signal for a
main track to be reproduced and the reproduction signals of one or
the other or both adjacent tracks based on light that is reflected
when said main track and said one or the other or both adjacent
tracks are irradiated with a light beam; a cross-talk removal
device of using a variable filter with a controllable coefficient
to extract the cross-talk from the reproduction of said one or the
other or both adjacent tracks and removing said cross-talk from the
reproduction signal of said main track; a coefficient control
device of controlling the coefficient of said variable filter using
a changeable control frequency zone; and a control frequency zone
setting device of determining the recording state of said one or
the other or both adjacent tracks and switching said control
frequency zone according to said recording state, wherein said
control frequency zone setting device sets said control frequency
zone to be wide for a specified period of time when the recording
state of said one or the other or both adjacent tracks changes from
an non-recorded state to a recorded state.
7. The data reproduction apparatus of claim 6 wherein said
coefficient control device is capable of switching said control
frequency zone between a first control frequency zone and a second
control frequency zone that is wider than said first control
frequency zone, and wherein said control frequency zone setting
device normally sets said first control frequency zone, and sets
said second control frequency zone for a specified period of time
when the recording state of said one or the other or both adjacent
tracks changes from an non-recorded state to a recorded state.
8. The data reproduction apparatus of claim 7 wherein said
specified period of time is the time required for said coefficient
to converge when said second control frequency zone has been
set.
9. The data reproduction apparatus of claim 6 wherein said control
frequency zone setting device determines the recorded state and
non-recorded state based on the amplitude of the reproduction
signals from said one or the other or both adjacent tracks.
10. The data reproduction apparatus of claim 6 wherein said control
frequency zone setting device sets said control frequency zone to
zero when the recording state of said one or the other or both
adjacent tracks changes from a recorded state to a non-recorded
state.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a cross-talk removal apparatus, which
removes cross-talk from adjacent tracks contained in the reproduced
signal of a main track based on reproduction signals from the main
track and from both adjacent tracks of a data recording medium; and
to a data reproduction apparatus that uses the cross-talk removal
apparatus when reproducing data from a data-recording medium that
has tracks.
2. Description of the Related Art
In the case of a large-capacity data-recording medium such as DVD,
there is a problem in that cross-talk from adjacent tracks affects
the reproduction signal from the main track being reproduced and
causes the reproduction quality to decrease. In order to solve this
problem, a cross-talk canceller has gained much attention, in which
three light beams are used to simultaneously reproduce three
adjacent tracks in order to obtain false cross-talk from the
reproduction signals of the adjacent tracks, and then the
cross-talk is removed by subtracting this cross-talk from the
reproduction signal from the main track.
This kind of cross-talk canceller irradiates three light beams on
the main track and both adjacent tracks and removes the cross-tack
according to the respective reproduction signals. In order to do
this, the cross-talk component is extracted by filtering the
reproduction signals of the two adjacent tracks using a digital
filter having a variable tap coefficient. This cross-talk canceller
must adaptively control the aforementioned tap coefficient in order
to follow changes in the cross-talk. This makes it possible to use
an optimum tap coefficient to properly remove the cross-talk from
the reproduction signal and to maintain the reproduction
quality.
Recently, writable data-recording media such as DCD-RAM has become
widely used. Normally, in the case of data-recording media such as
DVD-RAM it is assumed that the recorded areas and non-recorded
areas mixed together, so data are not necessarily recorded on the
adjacent tracks when reproducing the data on the main track. When
there are no data recorded on the adjacent tracks, there is no
cross-talk between the adjacent tracks and the main track, however,
when changing from having no data recorded on the adjacent tracks
to having data recorded, cross-talk between the adjacent tracks and
the main track occurs suddenly. In order to stably remove the
cross-talk that corresponds to this kind of change, it is preferred
that the tap coefficient of the cross-talk canceller be made to
follow the change.
However, since the control frequency zone is somewhat narrow,
control of the tap coefficient of the cross-talk canceller requires
time in order to converge. Normally, the control frequency zone for
the tap coefficient is set to be equal to or double the rpm of the
disk. This is because when the control frequency zone for the tap
coefficient is widened, the effects due to defects during
reproduction are received, and there is a possibility that the
cross-talk canceller will malfunction. Therefore, it is not
possible to widen the control frequency zone for the tap
coefficient and quickly change the characteristics of the
cross-talk canceller even though the adjacent tracks changed from a
state of having no data recorded to a state of having recorded
data. As a result, it is not possible to sufficiently remove the
cross-talk in the starting section of the recorded area, and thus
it is not possible to maintain good reproduction quality.
SUMMARY OF THE INVENTION
Taking into consideration the problems described above, it is the
object of this invention to provide a cross-talk removal apparatus
and data reproduction apparatus that are capable of quickly
removing cross-talk by switching the tap coefficient of a variable
filter, while at the same time obtaining a good reproduction
signal, when reproducing data from a recordable data-recording
medium, even though there are no data recorded on the adjacent
tracks.
The above object of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The
cross-talk removal apparatus that removes cross-talk from one or
the other or both adjacent tracks, which is contained in the
reproduction signal from a main track on a data-recording medium
that is to be reproduced, based on the reproduction signal from
said main track and the reproduction signals from said one or the
other or both adjacent tracks and is provided with: a cross-talk
removal device of using a variable filter with a controllable
coefficient to extract the cross-talk from the reproduction signal
of said one or the other or both adjacent tracks and removing said
cross-talk from the reproduction signal of said main track; a
coefficient control device of controlling the coefficient of said
variable filter using a changeable control frequency zone; and a
control frequency zone setting device of determining the recording
state of said one or the other or both adjacent tracks and
switching said control frequency zone according to said recording
state.
According to the present invention, the cross-talk, which is
extracted according to the reproduction signals from the main track
and both adjacent track when reproducing data on the data-recording
medium, is removed. In order to remove the cross-talk, a variable
filter is used whose tap coefficient is adaptively controlled.
Moreover, when controlling the coefficient of the variable filter,
the control frequency zone is switched according to the recording
state of the adjacent tracks. Therefore, in the case that there are
adjacent tracks on which no data are recorded mixed with adjacent
tracks on which data are recorded, it is possible to change the
control frequency zone over time in order to adequately correspond
with the changes in cross-talk. Therefore, for the variable filter
that is used when removing cross-talk the coefficient can be
controlled such that there is balance between followability and
stability in cross-talk removal.
In one aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The control
frequency zone setting device sets said control frequency zone to
be wide for a specified period of time when the recording state of
said one or the other or both adjacent tracks changes from an
non-recorded state to a recorded state.
According to the present invention, when it is determined during
removal of cross-talk that there are no data recorded on the
adjacent tracks at a specified time, and then it is determined that
there are data recorded, the control frequency zone for controlling
the coefficient of the variable filter is switched such that it is
wide, and that state is maintained for a specified period.
Therefore, when the state changes suddenly from a state of no
cross-talk to a state of increasing cross-talk, the speed of
convergence of the coefficient is increased making it possible to
quickly remove the cross-talk, and since there is control that
restores the state after becoming stable, it is possible to
suppress effects due to defects.
In another aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. the
coefficient control device is capable of switching said control
frequency zone between a first control frequency zone and a second
control frequency zone that is wider than said first control
frequency zone, and wherein, the control frequency zone setting
device normally sets said first control frequency zone, and sets
said second control frequency zone for a specified period of time
when the recording state of the one or the other or both adjacent
tracks changes from an non-recorded state to a recorded state.
According to the present invention, control is performed such that
normally a narrow first control frequency zone is set when removing
the cross-talk, and at the timing when the adjacent tracks change
from a state of having no data recorded to a state having data
recorded, the control frequency zone switches to a wide second
control frequency zone, and after that state has been maintained
for a specified time period, the control frequency zone returns to
the first control frequency zone. Therefore, it is possible to
selectively set the second control frequency zone temporarily at
timing when there is a need to increase the speed of convergence of
the coefficient, and this it is possible to quickly remove the
cross-talk using simple construction, while at the same time
suppress effects due to defects as described above.
In further aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The
specified period of time is the time required for said coefficient
to converge when said second control frequency zone has been
set.
According to the present invention, control is performed such that
when the control frequency zone has been switched and set to the
second control frequency zone, that state is maintained just long
enough for the coefficient to converge, so it is possible for the
coefficient to converge quickly, and after the coefficient has
become stable, it is possible to set the best control frequency
zone for preventing malfunction.
In further aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The control
frequency zone setting device determines the recorded state and
non-recorded state based on the amplitude of the reproduction
signals from said one or the other or both adjacent tracks.
According to the present invention, whether or not there are data
recorded on the adjacent tracks is determined according to the
amplitude of the reproduction signal obtained from the adjacent
tracks when removing cross-talk, and the control frequency zone is
set as described above to correspond to the judgment results, so it
is possible to accurately and quickly determine the recording state
of the adjacent tracks and properly set the control frequency
zone.
In further aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention.
The control frequency zone setting device sets said control
frequency zone to zero when the recording state of said one or the
other or both adjacent tracks changes from a recorded state to a
non-recorded state.
According to the present invention, when it is determined at a
specified time when removing cross-talk that there are data
recorded on the adjacent tracks and then next it is determined that
there are no data recorded, the control frequency zone for the
coefficient of the variable filter is switched to and set to zero.
Therefore, when then are no data recorded on the adjacent tracks,
the cross-talk removal operation ends, making it possible to
effectively prevent malfunction due to effect of defects.
The above object of the present invention can be achieved by the
data reproduction apparatus of the present invention. The data
reproduction apparatus that reproduces recorded data from a
data-recording medium on which tracks are formed and is provided
with: a reproduction device of generating a reproduction signal for
a main track to be reproduced and the reproduction signals of one
or the other or both adjacent tracks based on light that is
reflected when said main track and said one or the other or both
adjacent tracks are irradiated with a light beam; a cross-talk
removal device of using a variable filter with a controllable
coefficient to extract the cross-talk from the reproduction of said
one or the other or both adjacent tracks and removing said
cross-talk from the reproduction signal of said main track; a
coefficient control device of controlling the coefficient of said
variable filter using a changeable control frequency zone; and a
control frequency zone setting device of determining the recording
state of said one or the other or both adjacent tracks and
switching said control frequency zone according to said recording
state.
In one aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The control
frequency zone setting device sets said control frequency zone to
be wide for a specified period of time when the recording state of
said one or the other or both adjacent tracks changes from an
non-recorded state to a recorded state.
According to the present invention, when it is determined during
removal of cross-talk that there are no data recorded on the
adjacent tracks at a specified time, and then it is determined that
there are data recorded, the control frequency zone for controlling
the coefficient of the variable filter is switched such that it is
wide, and that state is maintained for a specified period.
Therefore, when the state changes suddenly from a state of no
cross-talk to a state of increasing cross-talk, the speed of
convergence of the coefficient is increased making it possible to
quickly remove the cross-talk, and since there is control that
restores the state after becoming stable, it is possible to
suppress effects due to defects.
In another aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The
coefficient control device is capable of switching said control
frequency zone between a first control frequency zone and a second
control frequency zone that is wider than said first control
frequency zone, and wherein
The control frequency zone setting device normally sets said first
control frequency zone, and sets said second control frequency zone
for a specified period of time when the recording state of said one
or the other or both adjacent tracks changes from an non-recorded
state to a recorded state.
According to the present invention, control is performed such that
normally a narrow first control frequency zone is set when removing
the cross-talk, and at the timing when the adjacent tracks change
from a state of having no data recorded to a state having data
recorded, the control frequency zone switches to a wide second
control frequency zone, and after that state has been maintained
for a specified time period, the control frequency zone returns to
the first control frequency zone. Therefore, it is possible to
selectively set the second control frequency zone temporarily at
timing when there is a need to increase the speed of convergence of
the coefficient, and this it is possible to quickly remove the
cross-talk using simple construction, while at the same time
suppress effects due to defects as described above.
In further aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The
specified period of time is the time required for said coefficient
to converge when said second control frequency zone has been
set.
According to the present invention, control is performed such that
when the control frequency zone has been switched and set to the
second control frequency zone, that state is maintained just long
enough for the coefficient to converge, so it is possible for the
coefficient to converge quickly, and after the coefficient has
become stable, it is possible to set the best control frequency
zone for preventing malfunction.
In further aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The control
frequency zone setting device determines the recorded state and
non-recorded state based on the amplitude of the reproduction
signals from said one or the other or both adjacent tracks.
According to the invention, whether or not there are data recorded
on the adjacent tracks is determined according to the amplitude of
the reproduction signal obtained from the adjacent tracks when
removing cross-talk, and the control frequency zone is set as
described above to correspond to the judgment results, so it is
possible to accurately and quickly determine the recording state of
the adjacent tracks and properly set the control frequency
zone.
In further aspect of the present invention can be achieved by the
cross-talk removal apparatus of the present invention. The control
frequency zone setting device sets said control frequency zone to
zero when the recording state of said one or the other or both
adjacent tracks changes from a recorded state to a non-recorded
state.
According to the present invention, when it is determined at a
specified time when removing cross-talk that there are data
recorded on the adjacent tracks and then next it is determined that
there are no data recorded, the control frequency zone for the
coefficient of the variable filter is switched to and set to zero.
Therefore, when then are no data recorded on the adjacent tracks,
the cross-talk removal operation ends, making it possible to
effectively prevent malfunction due to effect of defects.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram explaining the main construction of the
data reproduction apparatus of an embodiment of the invention;
FIG. 2 is a drawing showing the optical system of the pick up and
the irradiation state of the light beams for removing
cross-talk;
FIG. 3 is a block diagram showing the construction of the CTC unit;
and
FIG. 4 is a block diagram showing the construction of the
coefficient control unit of the CTC unit.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the invention is explained below based
on the drawings. In this embodiment, the case of applying the
invention to a data reproduction apparatus that has a cross-talk
removal apparatus and which reproduces an optical disk in DVD
format and outputs the user data is explained.
FIG. 1 is a block diagram explaining the main construction of the
data reproduction apparatus of this embodiment. The data
reproduction apparatus shown in FIG. 1 comprises a pick up 11, A/D
converters 12 to 14, CTC (Cross-Talk Canceller) unit 15, and CPU
16, and it reproduces user data that are recorded on the inserted
disk 10.
In the aforementioned construction, it is assumed that a writable
DVD disk such as DVD-RAM is used as the disk 10. Therefore, the
tracks on the disk 10 have areas that have recorded data mixed with
areas that do not have recorded data. In this case, it is necessary
to control switching the control frequency zone of the cross-talk
canceller as will be described below as a measure against sudden
changes in the effect of cross-talk from adjacent tracks.
The pick up 11 irradiates light beams onto the tracks of the
rotating disk 10, and generates a detection signals based on the
reflected light. Also, in this embodiment, three light beams from
the pick up 11 are irradiated onto three adjacent tracks of the
disk 10, and by removing the cross-talk between the main track
being reproduced and the adjacent tracks, the reproduction quality
is improved.
FIG. 2 shows the optical system of the pick up 11 and the
irradiation state of the light beams on the disk 10 for removing
cross-talk. As shown in FIG. 2, the optical system of the pick up
11 comprises: a laser 101, diffraction grating 102, beam splitter
103, object lens 104 and photo detector 105.
As shown in FIG. 2, in order to correspond to the land-group
recording format that is used for DVD-RAM, land tracks L and group
tracks G having different heights are alternately formed on the
data-recording surface of the disk 10. Normally, recording to the
disk is performed based on the phase-change method, and the crystal
state and reversible change of the recording material are used.
When writing to the disk 10 a recording mark M is formed on the
land track L or group track G. When it is possible to record to
both land tracks L and G tracks on the disk 10 in this way,
cross-talk from the adjacent tracks increases, so the need for the
cross-talk canceller also increases.
The example of FIG. 2 shows the state where there is a partially
recorded area having recording mark M on adjacent track T1. In
other words, with DVD-RAM it is possible to record at an arbitrary
recording position, so it can be assumed that there are recorded
areas mixed with non-recorded areas. In this case, cross-talk
increases suddenly during transition of the adjacent track T1 or T2
from a non-recorded state to a recorded state while tracing the
main track Tm and becomes a problem, however, this embodiment
handles this problem with the method described below.
In FIG. 2, the light beam B that is projected from the laser 101 is
separated into a main light beam Bm and two sub beams B1, B2 by the
diffraction grating 102. These three beams pass through the beam
splitter 103 and are irradiated onto the three adjacent tracks on
the data-recording surface of the disk 10 via the object lens 104.
The main beam Bm is irradiated onto the main track Tm and forms a
beam spot SPm. Also, one of the sub beams B1 is irradiated onto the
track T1 that is adjacent to the main track Tm and forms a beam
spot SP1, and the other sub beam B2 is irradiated onto the other
track T2 that is adjacent to the main track Tm and forms a beam
spot SP2. In FIG. 2, the main track Tm is the group track G, and
the adjacent traces T1, T2 are land tracks L.
The light that is reflected from the beam spot SPm from the main
beam Bm and the light that is reflected from the beam spits SP1,
SP2 from the sub beams B1, B2 pass through the object lens 104 and
are reflected by the beam splitter 103 and received by the
photo-detector 105. The photo-detector has a divided shape and the
respective reflected light beams are converted photo-electrically
and output as detection signals. The reproduction signal RFm (see
FIG. 1) for the main track Tm and the reproduction signals RF1, RF2
(see FIG. 1) for the two adjacent tracks T1, T2 are generated based
on the detection signals. The reproduction signals RF1, RF2 of the
two adjacent tracks T1, T2 become necessary when removing the
cross-talk component that is contained in the reproduction signal
Rm of the main track Tm.
In FIG. 2, it is preferred that the beam spot SPm from the main
beam Bm and the beam spots SP1, SP2 from the two sub beams B1, B2
be arranged in a straight line in the radial direction of the disk,
however, since the track pitch of the disk 10 is narrow, light
reflected from each beam spot must be received separately by
different detectors, so as shown in FIG. 2, each of the beam spots
SPm, SP1, SP2 are arranged in a diagonal straight line at specified
intervals in the tangential direction of the tracks. Therefore,
delays that corresponds to the intervals in the tangential
direction of the disk between the beam spots SPm, SP1, SP2 occur in
the three reproduction signals RFm, RF1, RF2. These delays are
corrected by the cross-talk canceller as described later.
Next, as shown in FIG. 1, the reproduction signals RFm, RF1, RF2
that are output from the pick up 11 are supplied to the A/D
converters 12 to 14. The A/D converter 13 samples the reproduction
signal RFm from the main track Tm and generates a sample-value
series Sm. Also, the A/D converter 12 samples the reproduction
signal RF1 from one adjacent track T1 and generates a sample-value
series S1, and A/D converter 14 samples the reproduction signal RF2
from the other adjacent track T2 and generates a sample-value
series S2. Each of the respective sample-value series Sm, S1, S2
that are generated by the A/D converters 12 to 14 are supplied to
the CTC unit 15.
As the means for removing cross-talk, the CTC unit 15 performs
specified operations on the aforementioned sample-value series Sm,
S1, S2, and generates a CTC output signal from which the effects of
cross-talk due to the adjacent tracks has been removed. The CTC
unit 15 is construction such that it can correct the delays that
exist between each of the reproduction signals RFm, RF1, RF2.
Details of the construction and operation of the CTC unit 15 will
be described later.
The CPU 16 functions as the means for performing overall control of
the reproduction operation of the data reproduction apparatus. The
CPU 16 controls the operation of the CTC unit 15, and sets the
optimum delay amount, which was found based on the jitter value for
example, for the CTC unit 15. Also, the CPU 16 references the
signal detection results from the CTC unit 15, and sends a
switching instruction to the CTC unit 15 to switch the control
frequency zone according to whether or not there is a signal on the
disk 10. Control of the CTC unit 15 for switching the control
frequency zone will be described later.
Next, the construction and operation of the CTC unit 15 will be
explained in detail. FIG. 3 is a block diagram showing the
construction of the CTC unit 15. As shown in FIG. 3, the CTC unit
15 comprises: delay circuits 201, 202, variable filters 203, 204,
coefficient-control units 205, 206 and adder/subtractor 207. With
the construction shown in FIG. 3, the sample-value series S2 that
corresponds to the adjacent track T2 is taken to be the reference,
and the delay of the sample-value series Sm that corresponds to the
main track Tm, and the delay of the sample-value series S1 that
corresponds to the adjacent track T1 are corrected.
In FIG. 3, the delay circuit 201 delays the sample-value series S1
that corresponds to the adjacent track T1 by a delay amount D1 set
by the CPU 16 and then outputs the series. Similarly, the delay
circuit 202 delays the sample-value series Sm that corresponds to
the main track Tm by a delay amount D2 set by the CPU 16, and then
outputs the series. Through the operation of these delay circuits
201, 202, it is possible to properly correct the delay due to the
spacing of the beam spots Sp1, Spm, Sp2 in the tangential direction
of the disk.
The delay circuits 201, 202 can be constructed, for example, using
FIFO memory. In other words, the sample-value series are input in
order to the FIFO memory, and data are delayed by using memory
space that corresponds to the delay amounts D1, D2.
The sample-value series S1' after delay correction variable filter
203 is shifted in order and input to the variable filter 203, which
performs a filtering operation using a variably controlled tap
coefficient, and calculates a cross-talk signal C1 that corresponds
to the cross-talk component from the adjacent track T1. Moreover,
the sample-value series S2 that corresponds to the adjacent track
T2 is shifted in order and input to the variable filter 204, which
performs a filtering operation using a variably controlled tap
coefficient, and calculates a cross-talk signal C2 that corresponds
to the cross-talk component from the adjacent track T2.
Next, the coefficient-control unit 205 controls the tap coefficient
of the variable filter 203 in order to correspond to the change in
cross-talk from the adjacent track T1. Similarly, the
coefficient-control unit 206 controls the tap coefficient of the
variable filter 204 in order to correspond to the change in
cross-talk from the adjacent track T2. A switching instruction from
the CPU 16 for switching the control frequency zone is input
together with the sample-value series S1, S2 and the CTC output
signal to the respective coefficient-control unit 205, 206. In this
embodiment, as the coefficient-control units 205, 206 control the
tap coefficient, switching control is performed for switching the
control frequency zone according to the recording state of the
adjacent tracks T1, T2, however that construction and operation
will be described in detail later.
The adder/subtractor 207 subtracts the cross-talk signal C1, which
corresponds to the adjacent track T1, and the cross-talk signal C2,
which corresponds to the adjacent track T2, from the sample-value
series Sm' that corresponds to the main track Tm and for which the
delay has been corrected, and outputs the aforementioned CTC output
signal. The CTC output signal that is obtained in this way, has
been filtered by an ideal filter and is a signal from which the
cross-talk components due to the adjacent tracks T1, T2 have been
removed.
Next, the construction and operation of the coefficient-control
units 205, 206 will be explained in detail. FIG. 4 is a block
diagram showing the construction of the coefficient-control unit
205. As shown in FIG. 4, the coefficient-control unit 205
comprises: a signal-detection unit 301, correlation-detection unit
302, pattern-detection unit 303, first correction-coefficient unit
304, second correction-coefficient unit 305, third
correction-coefficient 306, switch 307, and integrator 308. The
construction and operation of the coefficient-control unit 206 is
the same as that shown in FIG. 4, so only the coefficient-control
unit 205 is explained below.
In FIG. 4, the signal-detection unit 301 performs signal detection
in order to determine whether or not data have been recorded on the
adjacent track T1 based on the sample-value series S17 after delay
correction. The detection output from the signal-detection unit 301
is output to the CPU 16. It is possible to use various methods as
the signal detection method for the signal-detection unit 301, for
example, when the sample-value series S1' after delay correction
has an amplitude with zero as the center, the amplitude level of
the average absolute value of the sample-value series S1' after
delay correction can be compared with a specified threshold value.
In this case, the CPU 16 determines the frequency when the level
exceeds the threshold value based on the detection output from the
signal-detection unit 301, and finally can determine whether or not
data have been recorded on the adjacent track T1.
The sample-value series S1' after delay correction is input to the
correlation-detection unit 302, and it detects the correlation with
the detection signal that is output from the pattern-detection unit
303. On the other hand, the pattern-detection unit 303 detects the
zero-cross based on the signal pattern of the CTC output signal.
With the correlation-detection unit 302, it is possible to detect
the correlation by multiplying two input signals. By finding the
tap coefficient by correlating the sample-value series S1' after
delay correction and zero-cross of the CTC output signal in this
way, and then feeding the coefficient to the variable filter 203,
control is performed such that the aforementioned correlation
disappears, or in other words, such that the cross-talk component
is minimized.
The first correction-coefficient unit 304 multiplies the detection
signal from the correlation-detection unit 302 with a first
correction coefficient that corresponds to the normal control
frequency zone. Moreover, the second correction-coefficient unit
305 multiplies the detection signal from the correlation-detection
unit 302 with a second correction coefficient that corresponds to a
control frequency zone that is wider than the normal control
frequency zone. By using the first correction coefficient,
convergence of the tap coefficient becomes slower, and by using the
second correction coefficient, convergence of the tap coefficient
becomes quicker. In order to optimize the switching operation for
switching the control frequency zone (described later), it is
preferred that the second correction coefficient is set such that
it is about 4 times that of the first correction coefficient.
On the other hand, the third correction-coefficient unit 306
multiplies the detection signal from the correlation-detection unit
302 with a third correction coefficient that was set to zero. By
using the third correction coefficient the tap coefficient does not
change and the control frequency zone becomes zero.
The switch 307 performs the connection switching operation
according to the switching instruction from the CPU 16. In other
words, when using the normal control frequency zone, the switch 307
performs a switching operation that connects the side (a) of the
output signal from the first correction-coefficient unit 304, and
when using the wide control frequency zone, the switch 307 performs
a switching operation that connects the side (b) of the output
signal from the second correction-coefficient unit 305. Moreover,
when setting the control frequency zone to zero, as will be
described later, the switch 307 performs a switching operation that
connects the side (c) of the output signal from the third
correction-coefficient unit 306.
The CPU 16 as a rule performs control such that the first
correction-coefficient unit 304 is connected, however, when it is
determined based on the detection output from the signal-detection
unit 301 that the state of the adjacent track T1 has changed from a
non-recorded state to a recorded state, the CPU 16 performs control
such that the switch 307 switches to the second
correction-coefficient unit 305 at a specified timing when the
control frequency zone must be widened. Also, after a specified
amount of time elapses, it performs control such that the switch
307 switches again to the second correction-coefficient unit
304.
The integrator 308 integrates the output signal from the first
correction-coefficient unit 304 or the output signal from second
correction-coefficient unit 305 that is output via the switch 307,
and smoothly outputs the changing tap coefficient. The integrator
308 comprises a low-pass filter having specified dimensions and
cutoff frequency. When the dimension of the integrator 308 is
one-dimensional, the ratio of two control frequency zones is
proportional to the ratio of the first correction coefficient and
second correction coefficient.
The tap coefficient that is obtained by the coefficient-control
unit 205 as described above is supplied to the variable filter 203,
and this makes it possible to properly remove the cross-talk caused
by the adjacent track T1. Similarly, the tap coefficient that is
obtained by the coefficient-control unit 205 is supplied to the
variable filter 204, and this makes it possible to properly remove
the cross-talk caused by the adjacent track T2.
Next, the switching method for switching the control frequency zone
for the tap coefficient used by the CTC unit 15 during reproduction
of the disk 10 will be explained. When reproducing the disk 10, the
switch 307 is connected to the side of the first
correction-coefficient unit 304 as the default setting for the
coefficient-control units 205, 206. In this state, the CPU 16
monitors the detection output from the signal-detection unit 301 of
the coefficient-control units 205, 206, and when the CPU 16
determines that the state of the adjacent track T1 or T2 changes
from a non-recorded state to a recorded state, it switches the
switch 307 to the side of the second correction-coefficient unit
305. In this way, it is possible to widen the control frequency
zone for the tap coefficient of the CTC unit 15, and thus quicken
convergence to the proper tap coefficient, and makes it possible to
quickly remove the cross-talk.
On the other hand, after the control frequency zone has been
widened as described above, the CPU 16 waits for a fixed amount of
time, and then switches the switch 307 back to the side of the
first correction-coefficient unit 304. In other words, once the
coefficient becomes somewhat stable, the CPU 16 returns the control
frequency zone to its original state. For example, the tap
coefficient converges at about 5 times the time constant that is
determined by the second correction coefficient and characteristics
of the integrator 308, so this can be set as the fixed amount of
time mentioned above. After the switch has been switched back, the
control frequency zone for the tap coefficient of the CTC unit 15
becomes narrow, and the tap coefficient once again changes
gradually.
When the CPU 16 monitors the detection output from the
signal-detection unit 301 of the coefficient-control units 205, 206
and determines that the state of the adjacent track T1 or T2 has
changed from a recorded state to a non-recorded state, the CPU 16
switches the switch 307 to the side of the third
coefficient-correction unit 306. By doing so the control frequency
zone for the tap coefficient of the CTC unit 15 becomes zero and
the cross-talk canceller stops operating. In the normal
reproduction state, when there are no data recorded on the adjacent
tracks T1, T2, the cross-talk from the adjacent tracks T1, T2 is
mostly zero, so the tap coefficient converges to zero even when the
cross-talk canceller is operated using the first correction
coefficient for the normal zone. However, there is a possibility
that the tap coefficient could malfunction due to defects or the
like, so when the adjacent tracks T1, T2 are in a non-recorded
state, operation of the cross-talk canceller becomes stable by
stopping the operation of the cross-talk canceller. When the tap
coefficient becomes large due to malfunction, disk noise from the
adjacent tracks T1, T2 is added, and there is a possibility that
the signal from the main track Tm could become poor.
In the explanation above, the case of using the third correction
coefficient (zero) when the adjacent tracks T1, T2 are in the
non-recorded state was explained, however the tap coefficient of
the CTC unit 15 could also be reset to zero.
By controlling the control frequency zone for the tap coefficient
used by the CTC unit 15 in this way, it is possible to follow the
state of the adjacent tracks and very optimally maintain the
ability to remove cross-talk, even when there are mixed recorded
and non-recorded sections on the disk 10. Here, the timing for
widening the control frequency zone for the tap coefficient is only
for a short time at the beginning of a recorded area, so it is
possible to stably control the tap coefficient without being
affected by defects, and thus it is possible to stably remove the
cross-talk.
In the embodiment above, the case of applying the invention to a
data reproduction apparatus that reproduces data on an optical disk
that corresponds to DVD format, such as a DVD-ROM, was explained,
however, the invention is not limited to this, and it is possible
to widely apply to the invention to a data reproduction apparatus
that uses data recording media of other formats capable of
recording data.
In the explanation above, the signal-detection unit 301 determines
from the sample-value series S1' after delay correction whether or
not data have been recorded on the adjacent tracks T1, T2, however,
since this method takes a little time to perform signal detection,
it is also possible to determine from the sample-value series S1
before delay correction whether or not data have been recorded on
the adjacent tracks T1, T2.
Also, in the embodiment described above, the case of applying the
invention to construction using a light beam that is separated into
three light beams was explained, however, the invention is not
limited to this, and it is possible, for example, to apply the
invention to construction using a light beam that is separated into
five light beams.
According to the invention explained above, when reproducing data
from a recordable data-recording medium, switching of the control
frequency zone for the tap coefficient of a variable filter is
controlled according to the recording state of the adjacent tracks
even when the adjacent tracks change to a non-recorded state, so a
cross-talk removal apparatus that is capable of preventing
malfunction while quickly removing the cross-talk, and obtaining a
good reproduction signal is possible.
The entire disclosure of Japanese Patent Application No.
2001-131620 filed on Apr. 27, 2001 including the specification,
claims, drawings and summary is incorporated herein by reference in
its entirety.
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